The primary goal of the proposed research is to test the theory of X-chromosome inactivation with respect to the common forms of human, sex-linked color vision deficiencies, i.e., the protan and deutan conditions. The major prediction of the theory, known as the Lyon hypothesis, is that heterozygous females should have a retinal mosaic with normal patches cloned from the maternal X and mutant patches cloned from the paternal X. In terms of color vision, these patches should differ in spectral sensitivity owing to the lack or alteration of one of the cone photopigments in the mutant clones. The basic method is to measure spectral sensitivity across the retina with tiny stimuli presented on chromatic backgrounds designed to reveal the presence or absence of the normal cone photopigments. In order to minimize the small eye movements that would blur any underlying mosaic, a newly developed image stabilizer will be used that requires no attachment to the eye. In addition, color perception will be studied by having heterozygotes match spectral stimuli presented to normal and color-deficient patches. In this way it may be possible to discover what hues are perceived by protans and deutans. Finally, the possibility of ultra-fine mosaicism in the normal retina will be explored.